classloader¶

查看classloader的继承树，urls，类加载信息

classloader 命令将 JVM 中所有的classloader的信息统计出来，并可以展示继承树，urls等。

可以让指定的classloader去getResources，打印出所有查找到的resources的url。对于ResourceNotFoundException比较有用。

参数说明¶

参数名称	参数说明
[l]	按类加载实例进行统计
[t]	打印所有ClassLoader的继承树
[a]	列出所有ClassLoader加载的类，请谨慎使用
`[c:]`	ClassLoader的hashcode
`[c: r:]`	用ClassLoader去查找resource
`[c: load:]`	用ClassLoader去加载指定的类

使用参考¶

按类加载类型查看统计信息¶

$ classloader
 name                                       numberOfInstances  loadedCountTotal
 com.taobao.arthas.agent.ArthasClassloader  1                  2115
 BootstrapClassLoader                       1                  1861
 sun.reflect.DelegatingClassLoader          5                  5
 sun.misc.Launcher$AppClassLoader           1                  4
 sun.misc.Launcher$ExtClassLoader           1                  1
Affect(row-cnt:5) cost in 3 ms.

按类加载实例查看统计信息¶

$ classloader -l
 name                                                loadedCount  hash      parent
 BootstrapClassLoader                                1861         null      null
 com.taobao.arthas.agent.ArthasClassloader@68b31f0a  2115         68b31f0a  sun.misc.Launcher$ExtClassLoader@66350f69
 sun.misc.Launcher$AppClassLoader@3d4eac69           4            3d4eac69  sun.misc.Launcher$ExtClassLoader@66350f69
 sun.misc.Launcher$ExtClassLoader@66350f69           1            66350f69  null
Affect(row-cnt:4) cost in 2 ms.

查看ClassLoader的继承树¶

$ classloader -t
+-BootstrapClassLoader
+-sun.misc.Launcher$ExtClassLoader@66350f69
  +-com.taobao.arthas.agent.ArthasClassloader@68b31f0a
  +-sun.misc.Launcher$AppClassLoader@3d4eac69
Affect(row-cnt:4) cost in 3 ms.

查看URLClassLoader实际的urls¶

$ classloader -c 3d4eac69
file:/private/tmp/arthas-demo.jar
file:/Users/hengyunabc/.arthas/lib/3.0.5/arthas/arthas-agent.jar

Affect(row-cnt:9) cost in 3 ms.

使用ClassLoader去查找resource¶

$ classloader -c 3d4eac69  -r META-INF/MANIFEST.MF
 jar:file:/System/Library/Java/Extensions/MRJToolkit.jar!/META-INF/MANIFEST.MF
 jar:file:/private/tmp/arthas-demo.jar!/META-INF/MANIFEST.MF
 jar:file:/Users/hengyunabc/.arthas/lib/3.0.5/arthas/arthas-agent.jar!/META-INF/MANIFEST.MF

也可以尝试查找类的class文件：

$ classloader -c 1b6d3586 -r java/lang/String.class
 jar:file:/Library/Java/JavaVirtualMachines/jdk1.8.0_60.jdk/Contents/Home/jre/lib/rt.jar!/java/lang/String.class

使用ClassLoader去加载类¶

$ classloader -c 3d4eac69 --load demo.MathGame
load class success.
 class-info        demo.MathGame
 code-source       /private/tmp/arthas-demo.jar
 name              demo.MathGame
 isInterface       false
 isAnnotation      false
 isEnum            false
 isAnonymousClass  false
 isArray           false
 isLocalClass      false
 isMemberClass     false
 isPrimitive       false
 isSynthetic       false
 simple-name       MathGame
 modifier          public
 annotation
 interfaces
 super-class       +-java.lang.Object
 class-loader      +-sun.misc.Launcher$AppClassLoader@3d4eac69
                     +-sun.misc.Launcher$ExtClassLoader@66350f69
 classLoaderHash   3d4eac69